Understanding the molecular basis of developmental morphogenesis is fundamental to cell and evolutionary biology. It will also be a vital part of post-genomic biomedical techniques to address birth defects, cancer, and organ regeneration by achieving fine-scale control over the structure and function of living tissues at many levels. Direct exchange of chemical and electrical signals through gap junctions between cells controls migration, proliferation, and differentiation as a crucial part of normal physiology, embryonic development, and tumor progression. Ductin is a fascinating molecule with important roles in embryogenesis, cancer, viral infection, and neurotransmitter release. Ductin oligomers form the membrane sector of the H+ pump, and may also form gap junctions; however, the molecular mechanisms by which ductin mediates cell signaling and control events remain poorly understood. In particular, mice in which the ductin gene has been deleted die at day 4 of gestation - too early for meaningful analysis of what roles ductin plays in morphogenesis. In the context of our lab's mission - to unravel the mechanisms by which ion fluxes control biological shape, we are interested in the cell biology and embryology of ductin. Importantly, we have used pharmacological approaches in the frog embryo to show that a down-regulation of ductin activity disrupts the consistent left-right asymmetry of the visceral organs and heart. Left-right asymmetry is an important topic in basic developmental biology as well as biomedicine, since a variety of human syndromes result from errors in the patterning of the left-right axis. We also have strong preliminary data showing that ductin is present in the cell membrane (as well as the cytoplasm) of early embryonic blastomeres consistent with a gap junctional role for ductin. These findings are particularly interesting since our prior work has implicated H[unreadable] flux, endogenous voltage gradients, and gap-junctional communication in early LR patterning steps of chick and frog embryos. Thus, we propose to capitalize on well characterized and powerful techniques in highly-tractable model systems, Xenopus and chick, to achieve fundamental insight into the embryonic patterning role of ductin through four aims: (1) clone all ductin genes in chick and Xenopus and characterize in detail the embryonic and subcellular localization of mRNA and protein during early developmental stages; (2) test the hypothesis that ductin functions by providing a gap junctional path for LR signals; (3) test the hypothesis that ductin participates in establishment of the endogenous voltage gradient across the embryonic midline which drives asymmetric movement of LR morphogens; and (4) test the hypothesis that the intrinsic chirality of the cytoskeleton provides the initial asymmetric localization of ductin protein. By directly addressing the morphogenetic role of ductin, and the molecular mechanism by which it functions, we will rapidly make progress on a completely novel aspect of LR asymmetry, and begin to understand a protein at the nexus of the most important cellular events. [unreadable] [unreadable]